1. Field of the Invention
This invention relates to a liquid supplying device for supplying quantitatively various kinds of liquids such as sampler solutions, chemical reagents and other chemicals to a physical and chemical apparatus such as a liquid gas-chromatograph and or reaction analyzers.
2. Description of the Prior Art
In a liquid supplying device for use in physical and chemical apparatus, there has been generally used at least one proportioning pump such as a plunger pump, diaphragm pump and tubing pump.
The plunger pump has a liquid chamber defined between paired check valves for allowing liquid to pass in one direction and a plunger which moves to and fro within the liquid chamber so as to produce a unidirectional flow of the liquid. The diaphragm pump utilizes a diaphragm as a pressure generating means. As the check valve used in a pump of this type, there are a flap valve and a ball valve, for example.
The tubing pump produces a flow of liquid by utilization of succession of contraction waves on an elastic tube, the tube being repeatedly squeezed in one direction by means of a plurality of squeezing members operated by cams.
As conventional liquid supplying devices of the types other than the successively operated pumps as described above, there have been known a pump having a change-over valve for alternately switching liquid intake and outlet passages to each other so as to send out liquid introduced into a pump cylinder, and a pump having solenoid valves disposed respectively on liquid intake and outlet passages in place of the change-over valve mentioned above.
The aforenoted conventional liquid supplying devices using a plunger pump or diaphragm pump are suitable for supplying a small quantity of liquid, but requires at least one check valve. The use of such a check valve for controlling the flow of liquid in the liquid supplying device of this type entails a disadvantage such that it may possibly permit air bubbles to cling thereto so much as to decrease the amount of liquid being supplied. the operation of the valve may become unstable and further the inner pressure of the liquid flowing therethrough may vary with time in accordance with the change in size of the air bubbles resultantly produced, i.e. the so-called drift phenomenon in supplying liquid which causes the valve to be deactivated.
Since the check valve used in the pump is not operated at a constant speed with the pressure of the liquid supplied, the relation between the pressure and quantity of the supplied liquid cannot be maintained constant. This may disadvantageously lead to error in the quantity of the supplied liquid.
The tubing pump as noted above has a complicated mechanism for squeezing the elastic tube. Furthermore, this pump has problems such as inferiority in durability, pressure resistance and chemical resistance, and generation of pulsation flow of the liquid being sent out.
On the other hand, the liquid supplying devices using the change-over valves or other valves can solve the problems such as generation of air bubbles and inferiority in durability and pressure resistance as touched upon above, but cannot automatically control the momentum in one stroke of a piston used therein and the variation in operating rate according to a prescribed program. Therefore, the conventional liquid supplying devices of this type cannot be applied for the purpose of automatically pouring a given chemical reagent in a gas chromatograph, or combining a reagent and a reactant chemical to be poured to analyzers of various types.